The invention pertains to a process for activating a gate, more particularly a gate in a range where errors are expected in testing materials by the ultrasound method using the pulse echo process. The process incorporates a test head that emits diagonally onto the surface of the material to be tested. The invention pertains also to an apparatus that functions according to this process.
In the procedure of this kind that is already familiar from the publication DE-23 21 699 the input echo is employed for activating the expected error gate of the same test head. This publication demonstrates that such an echo start device tier an expected error gate can only function when the signal of the sound entrance echo is at least of a certain amplitude. Different ways of attaching the device to the surface of the material to be tested cause changes in the echo signal, however, and in addition, variations occur in the height of the signal in the portion of the sound emitted from the surface of the test material. In consequence, activation of the evaluation gate can be delayed to the extent of several ultrasound wave lengths.
Procedures of the above mentioned kind are also familiar from publications OS-41 50 577 and DE-30 17 900 C2. For general reference to this procedure see also the DE-publication "Ultrasonic Testing of Material" by J. and H. Krautkramer, 4th edition.
For test heads from which the impulse is emitted diagonally the procedure that is already familiar and the device that functions according to this procedure have not always led to reproducible results. In test heads of this kind a relatively small and also broad sound input register is frequently present. In consequence, the echo start conditions can not be conclusively realized under practical conditions because on the one hand the strong dynamic can lead to loss of the start incident because the echo remains smaller than a given threshold, for which reason the test is not concluded. On the other hand, by reason of the dynamic and the broad echo signals, the start point for the expected error range changes, for which reason the gate/aperture position varies.
The purpose of the invention is defined by these considerations, its aim being to improve the echo start steering for the aperture/gate position of an expected error range or of another time range in such a way that, for a test head from which the pulse is emitted diagonally, the best possible coordination between transmission of a sound impulse and activation of the time gate, e.g. an expected error range gate, is achieved.
As was demonstrated in procedural tests, this task is solved by a device for activating a time gate but especially an aperture for an expected error range in testing materials according to the impulse echo process; said device incorporates a test head which emits pulses that impinge horizontally on the surface of a test body that is characterized by the test head from which the pulses are emitted vertically and which is firmly connected to a test head on which pulses impinge vertically; said test heads transmit at given intervals ultra sound impulses which are subsequently received; and the echo impulse of the entry of the sound into the test head from which the pulses are emitted vertically is utilized to trigger the time gate of the test head from which the pulses are emitted diagonally.
With reference to the device, it was solved by a process characterized by a test head from which pulses emitted diagonally and a test head from which pulses transmitted in the main vertically are connected firmly together; and they are moveable relative to a test body; the receiver channel of the test head from which pulses are emitted vertically is fitted with a time gate for the input echo; this input echo, if necessary after traversing a time delay switch, is conducted as trigger signal of the time gate for an expected error range of the receiver channel of the test head from which pulses are emitted diagonally.
In essence, the invention is based on evaluating the sound entry display for an additional test head that is connected to the test head from which the pulse is received diagonally. The pulse of this additional test head is essentially vertical. When the ultrasound waves are introduced vertically it is usual to receive a high, narrow signal for the portion of the sound that is reflected at the surface of the test material. For this reason it is possible to tune more finely the starting point for the time gate and, in particular, the gate for the expected error range. The sound input echo for the test head from which the sound is emitted vertically is now introduced in order to determine the instant for activating the expected error gate for the test head from which the pulse is emitted diagonally. In most applications the sound input echo for the test head from which the pulse is emitted vertically is delayed by a given period of time. For devices that function cyclically the delay time is added.
The procedure that is in accord with the invention offers the advantage that the signal of the sound input echo is processed and can be prepared before it is required for activating the expected error gate. By reason of the present state of the technology, however, the entry signal continues to be processed in real-time, and under these conditions evaluation is to say the least difficult. As ultrasonic testing devices normally function cyclically, preparation and time delay for the pulse entry echo can be conducted simply because the processes proceed periodically.
Even though the process is described in the main for activating an expected error gate no limitation to the patent sought is implied. The process can just as well be employed for activating any other time gate, for example, a gate for a variable interference/suppression point, and in this connection reference is made to publication DE 38 22 699 AI. It can also be employed for measuring run time or the like. In place of the concept pulse-echo-process the word pulse-reflection-method is frequently employed since it has the same meaning.
It is normally not necessary to provide a separate test head from which the pulse is emitted vertically exclusively for the echo start of the time gate; instead, test heads which are present any way and from which the pulse is emitted vertically, such as for example test heads for determining the thickness of walls, or heads for ascertaining core faults, can be employed. In order to employ such test heads for the echo start of an expected error range of a test head from which the pulse is emitted diagonally they should impinge on the same surface point as the test head that impinges diagonally. Under these conditions, there occurs in a certain range of the lead advance a proportionality between forward run of the test head from which the pulse is emitted vertically and forward run of the test head from which the pulse is emitted diagonally. For this reason, changes in the forward run of the test head from which the pulse is emitted vertically can easily be transformed into changes in the forward run of the test head from which the pulse is emitted diagonally.
It has proved of great advantage in determining the sound entry echo to take into account in each instance at least the last known echo of the test head from which the pulse is emitted vertically. In devices that function cyclically the time of occurrence of the last known input echo is then incorporated in the event that the input echo of the test head from which the pulse is emitted vertically should fail. In this way the test is not interrupted. In order to obtain in this way the median position for the input echo it is especially advantageous if a roving median range results from the last echo time instants. Determining the gate in the expected error range becomes more stable because of this, which is to say that it wanders back and forth less with every test.